1. Field of the Invention
The present invention relates to a start-up method of a hydrocarbon synthesis reaction apparatus.
Priority is claimed on Japanese Patent Application No. 2012-247727 filed on Nov. 9, 2012, the content of which is incorporated herein by reference.
2. Description of Related Art
In recent years, as a process for synthesizing liquid fuels from natural gas, the GTL (gas-to-liquids: liquid fuels synthesis) technique has been developed. This GTL technique includes the steps of reforming a natural gas to produce a synthesis gas containing carbon monoxide gas (CO) and hydrogen gas (H2) as main components, synthesizing hydrocarbons using this synthesis gas as a feedstock gas and using a catalyst via the Fischer-Tropsch synthesis reaction (hereinafter also referred to as the “FT synthesis reaction”), and then hydrogenating and fractionating these hydrocarbons to produce liquid fuel products such as naphtha (raw gasoline), kerosene, gas oil and wax, and the like.
In a hydrocarbon synthesis reaction apparatus used in the GTL technique, a hydrocarbon is synthesized by FT synthesis reaction of carbon monoxide gas and hydrogen gas included in synthesis gas inside a reactor, which contains slurry having solid catalyst particles (cobalt catalyst and the like, for example) suspended in a liquid medium (liquid hydrocarbon and the like, for example).
FT synthesis reaction is an exothermal reaction and depends on temperature. The higher temperature is, the more FT synthesis reaction proceeds. In the case in which heat generated by the reaction is not removed, the temperature in the reactor increases rapidly by accelerating FT synthesis reaction, thereby causing thermal deterioration of the catalyst. The slurry is generally cooled via a heat exchanger tube by coolant flowing therethrough. In order to operate the reactor at a higher CO conversion ratio therein, wherein the CO conversion ratio is a ratio of an amount of CO expended in FT synthesis reaction to an amount of CO at an inlet of the reactor from which synthesis gas is introduced thereto, it is required to secure a large effective area of the heat exchanger tube, contacting with the slurry, for removing the heat from the slurry so as to cool the slurry efficiently. The heat exchanger tube is generally installed along the vertical direction of the reactor. Therefore, the effective area of the heat exchanger tube for removing the heat from the slurry depends on the liquid level of the slurry in the reactor. That is, the higher the liquid level of the slurry is in the reactor, the larger the effective area of the heat exchanger tube is.
In a commonly-performed start-up method for the reactor, the slurry is loaded into the reactor in an initial stage of the FT synthesis reaction in such a way that a liquid level thereof reaches the same level as that in a steady-state operation, in order to secure the larger effective area of the heat exchanger tube thereby increasing the CO conversion ratio rapidly.